In the industrial sector there is a plurality of spring-loaded braking systems where a spring force acts on brake elements via a power-reinforcing lever system, said brake elements, in turn, engaging a corresponding brake block (e.g. a disk or a drum). Such industrial brakes are made e.g. as disk brakes, drum brakes and also as barrel tensioners. They are widely used in the conveyor technique, e.g. in conveyor belt systems, crane systems, conveyor systems and hoisting systems, etc. They are usually designed as safety brakes and operate according to the fail-safe principle. This means that the brakes are designed in such a way that they are automatically applied in a breakdown, e.g. in the case of a power failure, and stop the moving parts to be decelerated as quickly as possible or keep them in a certain position (e.g. in the case of hoisting gears or elevators).
For this purpose, it is initially necessary to keep the brakes in an open, i.e. released, state. This is achieved by what is called brake release devices which, in an activated state, operate against the brake spring force, eliminate the latter, open the brake and keep it in the (open) released state. This is often achieved by electrohydraulic brake release devices which act on the brake lever arrangement in parallel to the brake spring.
They operate according to the following principle: For releasing, a drive (usually an electric motor) is set in motion. This drive acts on a rotary pump which, during operation, pressurizes and conveys a hydraulic medium which, in turn, acts on a cylinder piston surface that is coupled to the brake lever arrangement via an actuating rod. In this connection, a certain pressure acts on the actuating piston surface at a certain speed and said pressure, in turn, applies a certain actuating force to the arrangement and neutralizes the (restoring) force of the brake spring.
The pumps used in this connection are usually rotary pumps which have to be actuated in continuous operation when the brake is released. During braking, the drive is stopped, the rotary pump is at a stand-still and the hydraulic medium flows through the rotary pump back into a reservoir, the actuating cylinder is pushed back by the brake spring and the brake meshes or “is applied”.
Such brake release devices (cf. FIGS. 8A and 8B) have a simple configuration and offer a high operational reliability. However, they also have a number of drawbacks: The pressures which can be applied in continuous operation by means of rotary pumps are relatively low. As a result, the effective surfaces on the actuating pistons must be relatively large and therefore the required brake release devices also have to be relatively large. In continuous operation, the drives are continuously loaded and therefore have to be designed for very long operation times as well. In order to release a brake, relatively large volumes of hydraulic medium have to be moved. This prolongs the actuation cycles that can be realized, and therefore such brake release devices can only be used to a limited extent for very short release and braking intervals. In order to minimize the problems occurring on shaft seals in continuous operation, the electric motors are operated in a hydraulic medium (what is called wet runners). However, this means that, in order to maintain the motors, the hydraulic liquid must initially be fully removed. The continuous operation required for the release also causes thermal problems. In particular, the overall size, the weight and the problems existing in connection with the continuous operation are considered to be disadvantageous.
One approach may be to run a brake release device in intermittent operation, i.e. after building up a certain operating pressure on the cylinder, said pressure is kept constant via suitable switch valves and is reduced again during braking. However, this requires additional line and valve arrangements on the brake release device. Therefore, the object is to realize in a brake release device an intermittent operation which eliminates at least in part the above mentioned drawbacks.